Chemotherapeutic agents currently used for anti-tumour therapy are selected for their toxicity towards rapidly proliferating cells. Most of them cause undersirable systemic effects such as cardiac or renal toxicity, marrow aplasia, alopecia, nausea and vomiting. During the last few years, many authors have tried to eliminate these side effects by increasing the availability of the drug to the tumor site. Enzymes, radioisotopes, DNA, toxins, various macromolcules, and antibodies against fibrin or against tumour-specific surface antigens are bound to drugs in an attempt to increase the selectivity of the chemotherapeutic agents, or to decrease their toxic effects on normal cells (Rubens R. D., Lancet, 1974, 1, pp. 498-499; Gregoriadis G. et al., Res. Commun. Chem. Pathol. Pharm., 1975, 10, (2), 351-362).
The targeting of drugs to a tumour by antibodies to surface antigens may have considerable implications by increasing the therapeutic index.
It is recognized that the ideal antineoplastic drug would destroy cancer cells without adverse effects or toxicities on normal cells, but no such drug exists yet. However, despite the narrow therapeutic index of many drugs, treatment and even cure are possible in some patients.
Dactinomycin, doxorubicin and daunorubicin are all given rapidly intravenously and all cause tissue necrosis if extravasation occurs. When doxorubicin and daunorubicin are given rapidly intravenously, there is rapid dispersement throughout tissues and plasma. Their biological half-life is 30 min, with detectable plasma levels of doxorubicin up to 15 h. Both doxorubicin and daunorubicin are extensively metabolized by the liver, yielding active and inactive metabolites.
Daunorubicin is effective in treating acute leukemia. On the other hand, doxorubicin is one of the most active antineoplastics ever identified. In fact it is used to treat acute leukemia, Hodgkin's disease and non-Hodgkin's lymphomas, small cell and non-small cell lung cancer, cancers of the breast, ovaries, stomach, thyroid, and bladder, osteogenic and soft tissue sarcomas, and malignant melanoma. The side effects include nausea, vomiting, alopecia, myelosuppression, and dose-dependent cardiotoxicity (&gt;550 mg/m.sup.2).
The effectiveness of most anti-tumor agents is greatly reduced because of the nature of the illness and the high toxicity of those active products. It is believed that the problem of high toxicity of the anti-tumor agents can be circumvented by activating the anti-tumor agents with a chemical entity, thereby reducing the toxicity of these drugs without decreasing their effectiveness.
In U.S. Pat. No. 4,625,019, Relyveld, there is described the crosslinking agent of daunorubicin with glutaraldehyde to form a water insoluble polymeric complex wherein the insoluble fraction upon resuspension in an aqueous medium in the absence of glutaraldehyde will gradually release the desired anti-tumor agent in a soluble form. This method consists mainly in mixing together daunorubicin, an antibody and glutaraldehyde, which can combine in three different ways. The conjugates obtained comprise the following mixture of polymeric products:
______________________________________ 1- 33% Antibody - glutaraldehyde - Daunorubicin 2- 33% Antibody - glutaraldehyde - Antibody 3- 33% Daunorubicin - glutaraldehyde - Daunorubicin ______________________________________
wherein only the antibody-glutaraldehyde-daunorubicin conjugate is active. Furthermore, these three possible conjugates can be linked together by the excess glutaraldehyde in solution to form an agglomerate, which makes it difficult to isolate the active conjugate which is an autopolymerized anti-tumor agent.
This method is not readily reproducible and gives an unstable conjugate product. Unfortunately, this autopolymerized anti-tumor agent has the disadvantage of being insoluble in water and thus loses its specific activity against tumor cells. This insoluble product cannot be used intravenously for a systemic treatment since it is taken up by phagocytic cell such as monocytes, macrophages or cells. Finally, this product is not very stable and therefore does not have a very long shelf life.
Shen and Ryser (Biochem. Biophys. Res. Commun., 1981, 102, 1048) have reported the use of maleic anhydride (A) and cis aconitic anhydride (B) for the conjugation of daunorubicin on solid supports or proteins. ##STR2## These adducts do not have any pharmacological activity, since they release the drug at a pH of 4.0. The drug remains attached to these coupling agents at the physiological pH of 7.4.
It would therefore be highly desirable to have a conjugation agent which provides highly stable anti-tumor-conjugation agent-protein complexes which could release the drug at the targeted site under adequate physiological conditions. It would be also desirable, if such a product was stable at room temperature for a long period of time without having polymerization problems, and if such compounds could be handled by anyone having minimal knowledge of this subject matter instead of specialized personnel. It is also highly desirable that such conjugation agent decreases the toxicity of the drug while enhancing its effectiveness.
Furthermore, it would be of a great advantage if there could be provided intermediates of such compounds which would be stable for months at room temperature.